1. Field of the Invention
This invention pertains to a method for providing a conductive, non-stick coating at or near room-temperature to many materials which can benefit therefrom. More specifically, the present invention pertains to a method and apparatus for applying the conductive, non-stick coating to different materials, as well as presenting various embodiments which can take advantage of the coating's properties including bio-compatibility, flexibility, radio-opacity, diffusion resistance, wear and corrosion resistance, hardness, ability to be hydrophobic or hydrophilic, adherence to multiple materials, sterilizability, and chemical inertness and stability.
2. State of the Art
The present invention was originally developed as a result to improve electrosurgical instruments used in cauterization and other medical procedures, as well as to provide a bio-compatible coating for long-term implantable blood pumps. For example, prior U.S. patents have been issued for various electrosurgical blades which apply a non-stick coating to a cutting edge thereof. These blades typically suffered from small openings in the non-stick coating which were sometimes intentionally allowed to form in order to ensure electrical conductivity along the cutting edge. Exposing the metallic surface of the blade disadvantageously resulted in charred tissue sticking to these areas. The result was that the blade quickly became non-conductive and consequently unusable.
In an attempt to improve the blade, Blanch was granted U.S. Pat. No. 4,785,807 (the '807 patent) for teaching an electrosurgical blade which has a cutting edge of the blade which is abraded or etched, and a coat of a non-stick fluorinated hydrocarbon material which is applied over the etched cutting edge. A coating of non-stick material covers the surface area of the cutting blade and is intended to eliminate or reduce the clinging of charred tissue to the blade. By eliminating the small openings in the non-stick coating of previous blades, the blade better inhibited the build up of charred tissue. However, one drawback in the principle of the '807 patent is that the non-stick coating is not particularly durable, and will wear off after repeated usage. This is true partly because the non-stick and non-conductive coating has the properties of an insulator and had to be kept thin in order to enable the radio-frequency energy to pass through the non-stick coating to the tissue to cut and/or cauterize.
Another drawback of the blade described in the '807 patent is that the non-stick coating is not flexible. This inability to bend the electrosurgical blade seriously limits the options of the surgeon in the surgical procedures in which the blade can be used. Furthermore, bending the electrosurgical blade causes the non-stick coating to fracture. The electrosurgical blade then begins to rapidly build up charred tissue because of exposed etched metal of the blade, and any advantages of the non-stick coating are lost.
The non-stick coating of the '807 patent is also specifically described as Teflon (.TM.). The nature of Teflon (.TM.) is such that it requires a high current to be used in cutting and cauterization. This is because electrical current must pass through the Teflon (.TM.) to the tissue. However, this constant passage of current eventually breaks down the Teflon (.TM.), leaving small holes or other imperfections in the Teflon (.TM.) coating. Charred tissue then begins to adhere to the exposed metal beneath the Teflon (.TM.) coating. Furthermore, electrical current will no longer be uniform across the blade because the current will tend to concentrate at locations where the metal is exposed.
Another problem in the state of the art electrosurgical blades which utilize Teflon (.TM.) is that when heated, Teflon disadvantageously breaks down and evolves fluorine as a gas. This gas is hazardous to the patient and the surgical team.
The information above introduces some of the problems of other non-stick coatings. However, the problems are associated specifically with the issues which are involved when using the non-stick coating for electrosurgical instruments. There are actually numerous other embodiments of the present invention which are able to take advantage of the characteristics of the conductive, non-stick coating which was originally developed to solve problems relating to electrosurgical instruments, blood pumps, and other medical devices.
There are also other problems with state of the art medical devices which are made from materials which do not react well or ideally with body tissue. For example, stents can cause infection and thrombosis, and have lubricity problems. Stents also clot up after some period of time, and the body can form scar tissue around the stent. A bio-compatible coating having greater lubricity and which is flexible enough to expand with the stent when deployed. Stents also tend to stick to the catheter that is used to insert them.
Catheters also have lubricity problems. They can be difficult to insert, especially when they are long. They are also hard to extract because they can become stuck. Present coatings that are used on catheters usually do not remain on the catheter, and either have the property of bio-compatibility or lubricity, but not both. Nonbio-compatible coatings are usually inflexible and cannot be applied to flexing plastics such as catheters. Friction during insertion also removes biological and polymeric coatings, and they also wash off when exposed to flowing fluids, such as blood. The tip of the catheter and the insertions site also tend to be the site of blood clots. These problems are exacerbated for balloon catheters in which the balloon sticks to the tissue or tears, releasing potentially dangerous gases into the body.
It is also of interest to recognize that most catheters use a radio-opaque metal band to denote the catheter position using X-ray imaging. This band disadvantageously causes crimping of the catheter. The metal band is also known to slip along the length of the catheter, thereby causing false readings of the catheter position in the body. The metal band providing radio-opacity is also typically large. This can result in insertion and extraction problems for the catheter. The metal band can also irritate and damage the inner surface of the vessel through which the catheter is inserted.
Guide wires used to install catheters also have problems of lubricity because they provide a frictional surface which resists entry into and passage through tissue.
The installation of a shunt is a painful process because of the friction of the tissue. Furthermore, state of the art shunts are also limited in their useful lifespan because they tend to have bio-compatibility problems.
Needles such as those used in dialysis and for diabetics which are of large diameter can also cause substantial pain during insertion and cause significant tissue damage.
Silicone-based medical devices such as inhaler seals, laryngechtomy prostheses, and nasal tampons have several major problems. The solid silicone is sticky and rubbery, and thus these devices are hard to insert and withdraw due to lubricity problems. Some of these devices are also subject to infection and thrombosis.
Trocars are also medical devices which would benefit from a bio-compatible coating having a high degree of lubricity. Trocars are used to introduce larger-sized implants and/or surgical tools, especially for minimally invasive surgery. Like needles, they have friction problems and can cause damage at the site of insertion.
Soft tissue implants such as breast, penile, and testicular implants, as well as devices such as pulsatile mechanical blood pumps suffer from diffusion problems. In the case of breast implants, huge liability has been incurred from silicone leaking out and causing potential systemic harm to the body. In the case of blood pumps, their pumping gases and fluids leak out, with potentially harmful side effects, as well as inconvenience caused by additional implanted hardware to replace lost fluids and added cost and inconvenience to the patient who has to make repeated trips to the hospital. Also, body fluids leak in, causing the corrosion of components which eventually cause device failure. These corrosion problems are also faced by implantable electrodes, leads, and sensors such as those of pacemakers and defibrillators. Drug containers also have problems of corrosion and chemical reactions, especially with the newer and more potent drugs, as well as of diffusion of drugs through the container, including the rubber stoppers used as the caps of some drug containers.
It is also mentioned that syringe components such as plungers often get stuck or caught while pulling in fluid. Often, excessive force is used while expelling fluids. These situations all combine to reduce patient safety because of increased risk of injury.
These are also similar problems to contraceptive and OB/Gyn devices which have problems with infection, thrombosis, tissue growth and friction causing irritation and subsequent trauma to surrounding tissue. Likewise, grafts and cuffs such as vascular grafts and varicose vein cuffs have problems with infection and thrombosis. Electrodes, especially those used for esophageal pacing, fetal monitoring, spinal epidural, and for ablation have problems of assuring electrical conductivity to the skin.
A different problem is raised by electro medical devices which suffer from failures caused by inadequate electromagnetic interference (EMI) shielding. Often, this failure relates to the use of plastic and other non-metallic parts in the electrical assembly that cannot be easily shielded.
Non-medical devices have other problems as well that could be solved by a coating as described above. For example, magnets have hydrogen embrittlement and subsequent degradation problems. These problems are acute in the new high-strength rare-earth magnets (e.g. Neodymium Iron Boron). This happens because hydrogen diffuses into the material and causes failure. Hydrogen embrittlement is also a problem in the aircraft industry with titanium and other structural materials.
Another problem that could be solved with a coating as described above is the sticking inside of a mold. The molded part sometimes sticks to the mold, destroying the part or the mold. Molds are presently made primarily of metal or ceramics, which makes then very expensive to make.
Disk drives might also benefit from the present invention. Specifically, EMI problems and friction problems could be eliminated with a coating like the present invention.
Another industry which could benefit from such a coating is in footwear. Polyurethane-based soccer shoes suffer from degradation of the polymer caused by high humidity conditions and subsequent diffusion of water vapor across the membranes used in the shoe.
Integrated circuits suffer from problems of moisture and ion ingress which can result in failure of the circuit. Another problem is the diffusion of gold used in the gold/titanium ohmic contacts.
Magnetic media could also substantially benefit from such a coating. The degradation over time is often the result of high humidity conditions and physical wear of the material from contact with a read or write head.
Fiber optic conduits could also benefit because they suffer from the diffusion of gases and other fluids which causes their optical properties to degrade. Superconducting and photo diodes also suffer from diffusion barrier problems.
Fluid valves and solenoids also having sticking problems. Their moving parts tend to stick to their static components, resulting in intermittent or terminal component failure.
All of the problems described above can be alleviated to some degree, and even altogether eliminated in many cases by a coating which has the characteristics of being conductive, having a high degree of lubricity, providing bio-compatibility, flexibility, radio-opacity, diffusion resistance, wear and corrosion resistance, hardness, ability to be hydrophobic or hydrophilic, adherence to multiple materials, sterilizability, and chemical inertness and stability.